On Fri, Feb 06, 2015 at 02:48:34PM +0200, Peter Ujfalusi wrote:
> Hi,
>
> In case when hwmods are used in nested way the lockdep validator will print out
> a warning message about possible deadlock situation:
>
> [ 4.514882] =============================================
> [ 4.520530] [ INFO: possible recursive locking detected ]
> [ 4.526176] 3.14.30-00289-ge44872fdca8f-dirty #198 Not tainted
> [ 4.532285] ---------------------------------------------
> [ 4.537936] kworker/u4:1/18 is trying to acquire lock:
> [ 4.543317] (&(&oh->_lock)->rlock){......}, at: [<c002d2dc>] omap_hwmod_enable+0x2c/0x58
> [ 4.552109]
> [ 4.552109] but task is already holding lock:
> [ 4.558216] (&(&oh->_lock)->rlock){......}, at: [<c002d2dc>] omap_hwmod_enable+0x2c/0x58
> [ 4.566999]
> [ 4.566999] other info that might help us debug this:
> [ 4.573831] Possible unsafe locking scenario:
> [ 4.573831]
> [ 4.580025] CPU0
> [ 4.582584] ----
> [ 4.585142] lock(&(&oh->_lock)->rlock);
> [ 4.589544] lock(&(&oh->_lock)->rlock);
> [ 4.593945]
> [ 4.593945] *** DEADLOCK ***
> [ 4.593945]
> [ 4.600146] May be due to missing lock nesting notation
>
> What lockdep did not realizes is that the two oh is not the same hwmod object
> and we have taken different locks.
>
> One example of nested hwmod usage is on DRA7xx platforms, where McASP can be
> configured to use ATL clock as it's functional clock. In this case the
> pm_runtime_get/put_sync call will enable the mcasp hwmod and as part of this
> operation it will enable the needed clocks. Since ATL clock is needed, we will
> have another pm_runtime operation from the ATL clock enable callback which
> will take the atl hwmod's lock. This will be seen by lockdep as possible
> deadlock situation.
>
> In order to notify lockdep about this, we need to switch using _nested
> version of locking function and assign different subclass to those hwmods which
> could be used in nested way.
IFF struct omap_hwmod is always statically allocated; as I think the
__init on _register() mandates, you can use the below annotation.
---
arch/arm/mach-omap2/omap_hwmod.c | 1 +
arch/arm/mach-omap2/omap_hwmod.h | 2 ++
2 files changed, 3 insertions(+)
diff --git a/arch/arm/mach-omap2/omap_hwmod.c b/arch/arm/mach-omap2/omap_hwmod.c
index 9025ffffd2dc..222d654ad6fd 100644
--- a/arch/arm/mach-omap2/omap_hwmod.c
+++ b/arch/arm/mach-omap2/omap_hwmod.c
@@ -2698,6 +2698,7 @@ static int __init _register(struct omap_hwmod *oh)
INIT_LIST_HEAD(&oh->master_ports);
INIT_LIST_HEAD(&oh->slave_ports);
spin_lock_init(&oh->_lock);
+ lockdep_set_class(&oh->_lock, &oh->hwmod_key);
oh->_state = _HWMOD_STATE_REGISTERED;
diff --git a/arch/arm/mach-omap2/omap_hwmod.h b/arch/arm/mach-omap2/omap_hwmod.h
index 5b42fafcaf55..754bdfb3f811 100644
--- a/arch/arm/mach-omap2/omap_hwmod.h
+++ b/arch/arm/mach-omap2/omap_hwmod.h
@@ -689,6 +689,8 @@ struct omap_hwmod {
u8 _state;
u8 _postsetup_state;
struct omap_hwmod *parent_hwmod;
+
+ struct lock_class_key hwmod_key;
};
struct omap_hwmod *omap_hwmod_lookup(const char *name);
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